Context: Caesalpinia sappan and Ochna integerrima are two native plants of Thailand and distributed widely throughout the country. Recently, water extracts from the stem bark of C. sappan and O. integerrima were found to exhibit potently antibacterial property but the antibacterial mechanism of action toward target bacteria has not been investigated yet. Aims: To study time-kill kinetic and the mechanism of action of C. sappan and O. integerrima waterextracts toward target bacteria. Methods: The time-kill kinetic study of bacteriostatic or bactericidal activity against Gram-positive and Gram-negative pathogenic bacteria within 24 h experiment was conducted and the mechanism of action on cell morphology of the target bacteria by using scanning electron microscopy (SEM) were investigated. Results: Both of the C. sappan and O. integerrima water extracts possessed bacteriostatic or bactericidal activity toward six tested pathogenic bacteria. The bacteriostatic or bactericidal activity depending on bacterial strains and the test concentrations (0.5, 1 and 2 × MIC) of these two extracts to the tested bacteria were observed. The bactericidal activity against all of the tested bacterial was evinced at 2 × MIC. The morphological alterations of the target bacterial cells of changing the cell size (decreased and increased), cell lysis and having cell cavity were detected by SEM after the treatment with C. sappan and O. integerrima water extracts. Conclusions: The water extracts from the stem bark of C. sappan and O. integerrima exhibited bactericidal activity by changing the cell size, cell lysis and cell cavity of the tested bacteria cell morphology.

Two new indole alkaloids, 1-methylindole-7-methoxy-3-carboxaldehyde (2) and 7-methoxyindole-3-carboxaldehyde (4), together with 7-methoxyindole-3-carboxylic acid methyl ester (1) and 1-methylindole-3-carbaldehyde (3) were isolated from the fruiting bodies of wild Sanghuang mushroom Tropicoporus linteus (TL663). TLC, ¹H-NMR and LC-MS chemical profiles of this mushroom compared with other three genera of wild Sanghuang mushroom extracts were investigated. The TLC, ¹H-NMR and LC-MS profiles of TL663 and Sanghuangporus sanghuang (SS664) were similar and significantly different from other mushrooms. These two samples indicated the same TLC chromatograms by showing prominent bands of 1 − 4 when observed under UV 254 nm and having sharp aldehyde proton signals of 3-carboxaldehyde indole type in ¹H-NMR spectra. From LC-MS analyses, peaks of isolated compounds 1 − 4 and indole-3-carboxaldehyde (5) in TL663 extract and peaks of protocatechuic acid (6), caffeic aldehyde (7), caffeic acid (8) and 3,4-dihydroxybenzalacetone (9) phenolic acids in TL663 fraction were identified. Graphical Abstract